How to Test Electrolytic Capacitors

Kim LewisUpdated July 19, 2017

Capacitors are electrical components that store charge. They are normally made from two conductors separated by a non-conductor, called a dielectric, such as paper or glass. The conductors inside capacitors are called plates.

There are many types of capacitors. Electrolytic capacitors are polarised, so when they are used in a circuit, care must be taken to ensure that the positive lead is connected to the positive side of the voltage source. A multimeter with the ability to measure capacitance can be used to test an electrolytic capacitor.

Study the units of capacitance. Capacitance is measured in farads. However, components are commonly measured in microfarads (10^-6 farads) and picofarads (10^-12 farads).

Examine the electrolytic capacitor carefully. The amount of capacitance, as well as the maximum voltage it can be used with, is normally indicated on its body. To ensure that polarity is observed, the negative side is indicated, usually with a minus sign and a black stripe.

Switch the digital multimeter on and find the capacitance setting. This is usually shown by the letter "F" on its body. It may also be shown by the symbol for capacitance, which is two parallel bars.

Turn the knob and choose the setting that is equal to or higher than the value of the capacitor. If you do not know the value, choose the lowest setting.

Measure and record the capacitance. If there is a caps holder on the body, do this by inserting each lead into the proper slot. The leads must be long enough to fit firmly. Otherwise, use the alligator leads supplied with the multimeter, and place the red lead on the positive side of the capacitor and the black lead on the negative side.

Tip

Make sure the capacitor is discharged first before testing. This may be done by attaching a resistor across the two leads, or by following the directions given in the multimeter's manual. If you do not get a reading, adjust the knob on the multimeter until you do.

Warning

High-voltage capacitors such as those from radios or TVs may hold a dangerous charge even when not connected to a circuit. Never directly touch the leads of a high-voltage capacitor that is not discharged.

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About the Author

Kim Lewis is a professional programmer and web developer. She has been a technical writer for more than 10 years and has written articles for businesses and the federal government. Lewis holds a Bachelor of Science, and occasionally teaches classes on how to program for the Internet.